1. Field of the Invention
The present invention relates to a method for producing acrylic acid and more specifically, relates to a method for producing acrylic acid from acrylic acid solution at high yield.
2. Description of the Related Art
In a process for producing acrylic acid by carrying out the catalytic gas phase oxidation of propylene and/or acrolein, it has been known that Michael adducts such as the dimer to pentamer and oligomer of acrylic acid are generated as by-products by the action of heat and its catalyst at purification step, in addition to water, acids such as propionic acid, acetic acid and maleic acid, acetone, aldehydes such as acrolein, furfural and formaldehyde at catalytic gas phase oxidation reaction. These by-products become cause for preventing the stable operation of the production of acrylic acid and reducing the yield of acrylic acid as a desired product. Further, since acrylic acid is a easily polymerizing substance, there have been problems that the polymer of acrylic acid is prepared at a synthesis step of accompanying heating and a purification step such as distillation to cause blocking in an apparatus and product yield is reduced. Various technologies are proposed for solving the problems and stably and efficiently producing acrylic acid.
In the patent literatures 1 to 4 described later, there are described processes for producing acrylic acid that adopted a distillation purification process by which gaseous acrylic acid obtained by the catalytic gas phase oxidation is caught as an acrylic acid solution and by-products contained in the solution are removed by distillation. In these technologies, a process of suppressing the polymerization of acrylic acid and a process of decomposing the Michael adducts and collecting them as acrylic acid are also proposed.
For example, in U.S. Patent Application Publication No.2004015014 (JP-A-2004-51489, hereinafter, called as “Patent Literature 1”), it is described that a polymerization inhibitor is fed from the specific position of an absorption column and a distillation colon so that the polymerization inhibitor is uniformly dispersed and there is described a process of providing coolers between respective steps, suppressing the generation of polymers by cooling feed solution and further, decomposing acrylic acid oligomer (Michael adducts) using a thin-film evaporator and a thermal decomposing vessel to collect acrylic acid. In the specification of European Patent Application Publication No.0887334 (JP-A-11-12222, hereinafter, called as “Patent literature 2”) and JP-A-2003-160532 (hereinafter, called as “Patent Literature 3”), there is proposed a process of decomposing the Michael adducts using a reaction-distillation apparatus, a distillation column equipped with a thin-film evaporator and a thermal decomposing vessel and collecting acrylic acid. Further, in JP-A-2003-246765 (hereinafter, called as “Patent Literature 4”), there is described a process of decomposing acryl multimer (Michael adducts) contained in the bottom solution(effluent) of an acrylic acid purification column to acrylic acid and collecting it to improve the yield of acrylic acid.